I was trying some buffer overflow examples in my Fedora Core 3, and after hitting the wall for about 3 hours i found that fedora core 3 has a stack proctection (exec-shield) enabled, so one way to disable it is "sysctl -w kernel.exec-shield=0" or "echo 0 > /proc/sys/kernel/exec-shield".
(beware that now you machine is vulnerable to Buffer overflows).
Note: This also apply to Fedora Core 2.